eli5 how does nfc not need electricity?


I can’t wrap my brain around how nfc just “holds data” but doesn’t need power to transmit data? Like how do ID cards use nfc?

In: 6

It *does* need power to transmit data, but it doesn’t carry it with it. The reader supplies it.

The reader emits a radio signal which is picked up by a coil of wire in the NFC card or device, acting as an antenna. The signal in the antenna is electricity and it is this which powers the chip that does some calculations on a code sent to it, changing it in a way only the chip should be able to and sending it back out another antenna. The reader then picks up this response and based on its contents knows which card it is talking to.

There are at least a couple of main ways to do it.

The easiest one to understand is where the tag takes energy from the radio signal emitted by the reader. It then uses that energy to send data back. The tag has an antenna to harvest the energy and enough capacitance/inductance to store it briefly. The reader is both supplying data and supplying RF power to the tag.

The more difficult one to understand is “inductive coupling”. Essentially, the reader and the tag create a circuit, much like a circuit that contains a transformer. Except this transformer has no iron core; it has an air gap that takes the place of the core. Since both the reader and the tag are part of the same circuit, they can pass data back and forth.

It’s similar to the way phones can be charged wirelessly without needing a power cable. The device reading the NFC transmits the power to operate it, that’s why they need to be in close proximity.

it gets power just like wireless charger gives power to your phone.

the chip card has a long antenna inside that receives the wireless power, then transmits the signal.

NFC **does** need electricity. NFC cards /labels don’t have batteries because they are powered by the reader through induction (the same way wireless phone charging pads do it).

The reader has an moving magnetic field, sends a tiny amount of power to the card, just enough to get it to transmit a weak radio signal with data.